1. Field of the Invention
The present invention relates to a magnetic lens which makes it possible to magnify and observe a minute magnetic domain contained in an object. The present invention also relates to a reproducing apparatus and a reproducing method for an information recording medium including a magnetic recording layer. In particular, the present invention relates to a magnetic reproducing element, a reproducing apparatus, and a reproducing method which make it possible to perform reproduction from an extremely minute magnetic domain while amplifying intensity of a reproduced signal.
2. Description of the Related Art
In recent years, the magneto-optical recording medium attracts the attention, which makes it possible to record a large amount of data at a high density and quickly perform recording and reproduction thereon, corresponding to the advance of multimedia. For example, the recording is performed on a magneto-optical recording medium capable of overwrite such that a laser beam is radiated onto the magneto-optical recording medium, and a magnetic field corresponding to input information is applied to a position irradiated with the laser beam. When the reproduction is performed on the magneto-optical recording medium as described above, a laser beam, which is weaker than that used upon the recording, is radiated onto the magneto-optical recording medium. Information is reproduced by detecting a polarization angle of a reflected laser beam depending on the direction of recording magnetization possessed by the returning light beam of the laser beam.
As shown in FIG. 20, a head mechanism, which is used for such a magneto-optical recording and reproducing apparatus, has been hitherto based on the use of an optical head 80 and a magnetic head 81 which are arranged on both sides of a disk recording medium respectively while opposing to one another with respect to the center line. In this arrangement, each of the optical head 80 and the magnetic head 81 has a large size and a large weight. Therefore, the respective heads 80, 81 are supported by a support member 83. A screw rotary shaft 84 is rotated by a driving motor 87, and thus the respective heads 80, 81 are moved over the disk recording medium 130 to record, reproduce, and erase the information. This system involves the following drawback. That is, the volume and the weight of the recording and reproducing apparatus are large, and it is impossible to respond, for example, to the demand for the small size, the light weight, the large capacity, and the high speed access upon recording, reproduction, and erasing which are required for the disk recording medium and for the recording and reproducing apparatus. On the other hand, a magneto-optical head mechanism 20 shown in FIG. 21 is known as a technique to respond to the miniaturization of the recording and reproducing apparatus by integrating the optical head 80 and the magnetic head 81 into one unit. In this mechanism, a driving unit 73 for an objective lens 301 of an optical head system 72, and a magnetic head slider 75 arranged with a magnetic head coil 76 are combined into one unit. A hole 77 is formed through the magnetic head slider 75 for transmitting a convergent light beam 74 of a laser beam 71 radiated from the optical head. The recording and reproducing apparatus based on the use of such a magneto-optical head has a considerably small volume. However, such an apparatus is insufficient to respond, for example, to the demand for the small size, the light weight, the large capacity, and the high speed access upon recording, reproduction, and erasing which are required for the recording and reproducing apparatus.
On the other hand, the magnetic hard disk is capable of rewriting recorded information. The magnetic hard disk is a recording medium having a large storage capacity and having high reliability. Therefore, the magnetic hard disk is practically used, for example, as a memory for the computer. However, the amount of information increases at a high speed, and the development of compact systems advances at a high speed as well. It has been attempted to achieve recording at a higher density on the magnetic hard disk based on a method to perform reproduction by using the laser beam.
In order to increase the recording density of the magneto-optical recording medium, it is necessary to make the recording magnetic domain to be minute. The magnetic field modulation method is used for the recording on the magneto-optical recording medium, in which a magnetic field having a polarity corresponding to a recording magnetic domain signal is applied to a temperature-raised portion while irradiating the recording medium with a laser beam. This method is capable of overwrite recording, and it has succeeded in high density recording, for example, recording with a shortest mark length of 0.15 xcexcm. Further, the light modulation recording system is also practically used, in which the recording is performed by radiating a power-modulated laser beam corresponding to a recording signal under a constant applied magnetic field. However, this method involves a problem concerning the resolution of an objective lens included in an optical head to be used when recorded minute recording magnetic domains are subjected to reproduction. The resolution has a limit value which is determined by the wavelength of the laser beam used upon reproduction and the numerical aperture N.A. of the objective lens. Reproduction is not achieved with minute magnetic domains of 0.15 xcexcm as described above.
For example, as for minute recording magnetic domains or minute concave/convex pits to be subjected to high density recording, a minute mark having a magnetic domain length of 0.15 xcexcm can be subjected to recording by using, for example, a laser beam having a spot diameter of 1 xcexcm. However, in the present circumstances, it is impossible to perform reproduction while distinguishing minute magnetic domain signals of 0.15 xcexcm by using the laser beam having the spot diameter of 1 xcexcm as described above. An approach has been suggested in order to eliminate the limitation of the reproducing resolution due to the optical spot diameter of the reproducing light beam, i.e., for example, the magnetically induced super resolution technique (MSR) as described, for example, in Journal of Magnetic Society of Japan, Vol. 17, Supplemental S1, pp. 201 (1993). This technique utilizes the fact that the temperature distribution appears on a magnetic film within a reproducing light spot when the magneto-optical recording medium is irradiated with a reproducing light beam, so that a magnetic mask is generated in the spot to reduce the effective spot diameter which contributes to the reproduction of the signal. The use of this technique makes it possible to improve the reproducing resolution without reducing the actual reproducing light spot diameter. However, in this technique, the amount of light, which contributes to the reproduction output, is lowered, and the reproduction C/N is lowered corresponding thereto, because the effective spot diameter is decreased by using the magnetic mask. As a result, it is difficult to obtain sufficient C/N, and hence it is difficult to practically use this technique.
Japanese Patent Application Laid-Open Nos. 1-143041, 6-295479, and 8-7350 disclose a method which uses a magneto-optical recording medium obtained by forming and stacking a magneto-optical recording layer and a recording magnetic domain-reproducing layer for transferring and magnifying recording magnetic domains to perform reproduction. However, in the case of the method described in each of the patent documents, the medium structure of the magneto-optical recording medium is complicated, and the production cost becomes expensive as well. Further, when the recorded magnetic signal is transferred to the reproducing layer, any noise such as leak magnetic field other than the reproducing magnetic signal is simultaneously transferred. As a result, the noise is contained in the magnified reproduced signal obtained from the reproducing layer. Therefore, there is a possibility that C/N of the magnified reproduced signal may be decreased.
The present invention has been made in order to solve the problems as described above, an object of which is to provide a magnetic reproducing element, a reproducing apparatus, and a reproducing method which make it possible to perform reproduction at high C/N from minute magnetic domains.
Another object of the present invention is to provide a novel element which makes it possible to magnetically magnify and observe minute magnetic domains contained in an object.
According to a first aspect of the present invention, there is provided a magnetic lens for magnifying a minute magnetic domain existing in an object to observe or detect it, the magnetic lens comprising:
a magnetic slit which is filled with a magnetic material and to which the minute magnetic domain is transferred; and
a detecting section including a magnetic film having a width larger than the minute magnetic domain at least a part of the magnetic film being magnetically connected to the magnetic slit, wherein:
magnetization information of the minute magnetic domain is detected from the detecting section on the basis of a magneto-optical effect by disposing the magnetic lens close to the object and radiating a light beam onto the magnetic film of the detecting section of the magnetic lens.
The existing optical lens is an element capable of visually magnifying a sample to perform observation. On the other hand, the device (or the element) of the present invention is a novel device capable of magnetically magnifying the minute magnetic domain contained in the object to perform observation. Therefore, the device can be regarded as a magnetic lens which is a concept corresponding to the optical lens. The device is herein referred to as xe2x80x9cmagnetic lensxe2x80x9d. Preferably, the object to be subjected to the observation is, for example, a magnetic recording medium and a magneto-optical recording medium on which magnetization information is recorded at a high density. These media have been developed in order that the recording magnetic domain is miniaturized to make it possible to perform high density recording. The magnetic lens of the present invention is extremely effective to detect the magnetization information recorded on such a minute magnetic domain. However, the magnetic lens of the present invention is not limited to the use for such a recording medium. The magnetic lens of the present invention is effective in all of the use or application to detect information containing magnetic characteristics in a minute area. For example, the magnetic lens of the present invention will be also effective to inspect or test integrated circuits such as LSI and microdevices provided with functions relevant to various magnetic characteristics.
When the minute magnetic domain of the object is observed by using the magnetic lens of the present invention, the magnetic lens is allowed to make approach to the object so that the magnetic slit of the magnetic lens is at a distance capable of detecting the leak magnetic field from the minute magnetic domain. In this state, the magnetization information on the minute magnetic domain is transferred to the magnetic slit by the aid of the leak magnetic field from the minute magnetic domain. When the light beam is radiated onto the magnetic film of the detecting section of the magnetic lens, the magnetization, which has been further transferred from the magnetic slit to the magnetic film of the detecting section, is detected in accordance with the magneto-optical effect of the magnetic film. The width (diameter) of the magnetic slit is designed so that it has a size not more than several times that of the minute magnetic domain intended to be observed. Preferably, the width is designed to be smaller than the minute magnetic domain. For example, the width is designed to be not more than 5 xcexcm, preferably not more than 0.2 xcexcm. Accordingly, only the magnetization information of a desired magnetic domain can be transferred to the magnetic slit while distinguishing the desired magnetic domain from the other magnetic domains adjacent to the minute magnetic domain intended to be observed. The magnetic film of the detecting section is larger than the width (diameter) of the minute magnetic domain. For example, the magnetic film has an areal size which is not less than twice the width of the minute magnetic domain, for example, several times to several tens times the width of the minute magnetic domain. Therefore, the magnetization information, which has been once transferred to the magnetic slit, is further transferred to the magnetic film having the large areal size as described above. Therefore, the magnetization having the magnetization information is magnified as compared with the minute magnetic domain. The magnetic film having the large areal size can be irradiated with the light beam to detect the magneto-optical effect (Kerr rotation angle) of the magnetic film by the aid of the reflected light beam. The signal intensity, which is obtained in this process depending on the magneto-optical effect, is amplified in accordance with the areal size ratio of the magnetic film with respect to the minute magnetic domain, as compared with the signal intensity obtained when the light beam is directly radiated onto the minute magnetic domain to detect the magneto-optical effect. Therefore, the use of the magnetic lens of the present invention makes it possible to observe the minute magnetic domain with the signal intensity sufficient to distinguish the magnetization information. The magnetic slit may be composed of permalloy having small coercive force.
The magnetic lens of the present invention may further comprise a non-magnetic layer provided between the magnetic slit and the magnetic film, wherein the magnetic slit and the magnetic film are magnetostatically coupled via the non-magnetic layer. The non-magnetic layer may be a reflective layer for reflecting the light beam radiated onto the detecting section. A material, which has higher thermal conductivity than a material for constructing the reflective layer, may be embedded in a portion of the reflective layer opposing to the magnetic slit. By doing so, the heat, which is generated by the light beam in the magnetic slit, is easily transmitted. Thus, the coercive force of the magnetic slit is lowered, making it easier to transfer the minute magnetic domain to the magnetic slit.
In the magnetic lens described above, the magnetic film may be a magnetic film which changes from an in-plane magnetizable film to a perpendicularly magnetizable film at a temperature above a predetermined critical temperature. In this arrangement, the magnetic domain, which has been transferred to the magnetic slit, is transferred to an area in which the temperature exceeds the critical temperature by being heated by irradiation with the light beam.
The magnetic lens may further comprise a reflective layer, and the magnetic slit may be embedded in the reflective layer. When the light beam is radiated, the reflective layer makes it possible to increase the reflected light beam from the magnetic layer.
According to a second aspect of the present invention, there is provided a magnetic reproducing element to be arranged closely to a recording medium, for performing reproduction on the recording medium including a magnetic recording layer recorded with information as a recording magnetic domain, the magnetic reproducing element comprising:
a magnetic transfer section composed of a magnetic material for transferring the recording magnetic domain thereto; and
a reproducing section composed of a magnetic material and magnetically connected to the magnetic transfer section, the reproducing section having a width larger than the recording magnetic domain, wherein:
a reproducing light beam is radiated onto the reproducing section when the information is reproduced, and the reproducing light beam is used to reproduce magnetization information transferred from the recording magnetic domain to the reproducing section via the magnetic transfer section.
The magnetic lens of the present invention can be used as a reproducing element for performing reproduction from the recording magnetic domain (minute magnetic domain) on the recording medium provided with the magnetic recording layer. Also in this case, when the reproducing section is irradiated with the light beam, the magnetization information on the recording magnetic domain is transferred via the transfer section to the magnetic film of the reproducing section to give the magnetic domain having the width larger than that of the recording magnetic domain. The transferred magnetization information is detected by the aid of the reproducing light beam on the basis of the magneto-optical effect. The transfer section may have a size smaller than that of the recording magnetic domain.
According to a third aspect of the present invention, there is provided a reproducing apparatus for performing reproduction on a recording medium including a magnetic recording layer recorded with information as a recording magnetic domain, the reproducing apparatus comprising:
an optical head for radiating a reproducing light beam onto the recording medium; and
a magnetic head for being arranged closely to the recording medium, wherein:
the magnetic head includes a magnetic transfer section composed of a magnetic material for transferring the recording magnetic domain thereto, and a reproducing section composed of a magnetic material and magnetically connected to the magnetic transfer section, the reproducing section having a width larger than the recording magnetic domain; and
the reproducing light beam is radiated from the optical head onto the reproducing section of the magnetic head when the information is reproduced, and the reproducing light beam is used to reproduce magnetization information transferred from the recording magnetic domain to the reproducing section via the magnetic transfer section.
The magnetic lens of the present invention can be applied to the magnetic head to be used for the reproducing apparatus for performing reproduction on the recording medium, for example, the magneto-optical recording medium or the magnetic recording medium provided with the magnetic recording layer in which the information is recorded as the recording magnetic domain. The reproducing apparatus of the present invention makes it possible to detect the minute magnetic domain recorded at a high density, with the increased signal intensity. Therefore, it is unnecessary for the magneto-optical recording medium to have the magnifying function composed of the complicated stacked structure as disclosed in Japanese Patent Application Laid-Open Nos. 6-295479 and 8-7350. Accordingly, it is possible to simplify the structure of the magneto-optical recording medium. Thus, it is possible to provide the magneto-optical recording medium at low cost, capable of performing the high density recording and reproduction thereon.
In the reproducing apparatus described above, the magnetic head is arranged closely to the recording medium so that the leak magnetic field from the recording magnetic domain may be detected to transfer the magnetization information on the recording magnetic domain to the transfer section. The reproducing apparatus of the present invention may further comprise a slider which floats over a surface of the recording medium in accordance with an aerodynamic action. In this arrangement, the magnetic head may be provided in a through-hole formed in the slider. A light-transmitting section may be formed in the slider. The tracking can be performed for the recording medium by using the light beam passed through the light-transmitting section. The light-transmitting section may be a through-hole, or it may be installed with a light-transmissive material, for example, a material such as GGG. A magnetic coil for applying a magnetic field to the recording medium may be provided in the slider. Further, there may be provided a first arm for supporting the optical head, and a second arm for floating and supporting the slider over the surface of the recording medium. The second arm may be joined to the first arm.
According to a fourth aspect of the present invention, there is provided a reproducing method for performing reproduction on a recording medium including a magnetic recording layer recorded with information as a recording magnetic domain, the reproducing method comprising the steps of:
providing a magnetic reproducing element comprising a magnetic transfer section composed of a magnetic material for transferring the recording magnetic domain thereto, and a reproducing section composed of a magnetic material and magnetically connected to the magnetic transfer section, the reproducing section having a width larger than the recording magnetic domain;
arranging, upon the reproduction of the information, the magnetic reproducing element closely to the recording medium so that magnetization information on the recording magnetic domain is transferred to the magnetic transfer section of the magnetic reproducing element by the aid of a leak magnetic field from the recording magnetic domain in the recording medium; and
radiating a reproducing light beam onto the reproducing section of the magnetic reproducing element to reproduce the magnetization information transferred from the recording magnetic domain to the reproducing section via the magnetic transfer section on the basis of a magneto-optical effect of a magnetic layer.
In the case of the conventional reproducing method for the magneto-optical recording medium, the magneto-optical effect of the magneto-optical recording layer has been detected by using the reproducing light beam by irradiating the magneto-optical recording medium with the light beam. However, in the novel reproducing method of the present invention, it is unnecessary to radiate the light beam onto the magneto-optical recording medium. In the method of the present invention, the recording magnetic domain of the recording medium is transferred to the magnetic transfer section of the magnetic reproducing element by utilizing the leak magnetic field. The magnetic domain (magnetization information), which has been transferred to the transfer section, is further transferred to the magnetic film of the detecting section having a large areal size. The magnetic domain transferred to the magnetic film is irradiated with the light beam, and the magneto-optical effect of the magnetic film is detected from the reflected light beam therefrom. Thus, the magnetization information contained in the minute magnetic domain in the recording medium can be reproduced with sufficient signal intensity. The reproducing light beam may be a continuous light beam or a pulse light beam. Further, a reproducing magnetic field may be applied when the information is reproduced in order to facilitate the transfer of the magnetization information to the transfer section and the magnification of the magnetic domain in the detecting section.
In the reproducing apparatus and the reproducing method according to the present invention, the recording medium may be a magneto-optical recording medium comprising at least a magneto-optical recording layer as the magnetic recording layer and a substrate, wherein the recording medium is arranged so that the magneto-optical recording layer is disposed nearer to the magnetic reproducing element than the substrate. In order to detect the leak magnetic field of the magneto-optical recording layer, it is necessary that the magnetic transfer section approaches the magneto-optical recording layer as closely as possible. Therefore, the arrangement as described above is preferred.